The present invention relates to combustion products detectors and, in particular, to an outer electrode with improved smoke entry.
Devices for detecting combustion products, such as smoke, are principally of two types, ionization type detectors and photoelectric detectors. In an ionization type detector, a conductive housing forms the outer electrode, as disclosed in U.S. Pat. No. 4,258,261 issued on Mar. 24, 1981.
The outer electrode must allow the entry of combustion products such as smoke into the interior of the electrode for detection. The larger the slots the more readily smoke can enter the electrode. However, with the increased size of the slots, high air velocity and static electricity can also enter the electrode more readily.
High air velocity and static electricity can adversely affect the smoke detection capabilities of the unit. In ionization type detectors, a minute electrical current is developed between two collector plates which is diminished when the smoke particles are in the ionized space and impede passage of the ions. However, when high velocity air passes into the electrode and carries out the ions, a spurious fire signal can be given by the detector as it simulates the reduced current flow caused by entrance of particles of combustion. Static electricity can likewise cause spurious fire signals to occur.
Therefore, a compromise must be reached to allow maximum smoke entry while minimizing the undesirable outside influences of high air velocity and static electricity.